I have a 73 MACH 1 invoice for my car I purchased years and years ago from Lois Emminger. It has the suggested retail price of 3088.00 and a sale amount of 2624.11.
This price included: Trim rings w/hub caps,dual racing mirrors,competition suspension,color-keyed carpeting,and all-vinyl buckets seats(it came with a standard interior, not the MACH 1 interior.
351 CID 4V 8 cylinder-retail 107.00 billed for 90.94
black 3/4 vinyl roof-retail 52.35 billed 44.50
four-speed manual
trans with Hurst shifter-retail 192.99 billed 164.04
I have more if this is what your looking for.
This was prepared 4/24/1973
The base for the mustang fastback was 2624.11.
It was delivered as a Q-code MACH 1 after options.
hope this helps!